1. Field of the Invention
This invention relates to a method and apparatus for preparing 3-[N-(2-aminoethyl)]aminopropylalkoxysilanes useful as silane coupling agents or the like.
2. Prior Art
As is well known in the art, 3-[N-(2-aminoethyl)]aminopropylalkoxysilanes are widely used as silane coupling agents and effective for various modification purposes, for example, improving adhesion at the organic-inorganic interface, tailoring various resins and modifying surfaces.
For the synthesis of these compounds, one typical method is discloses in U.S. Pat. No. 2,971,864, Polish Patent No. 145,671, and J. Org. Chem., vol. 36, No. 21 (1971), 3120-3126, as reacting 3-chloropropylalkoxysilanes with ethylene diamine to form 3-[N-(2-aminoethyl)] aminopropylalkoxysilanes. This method is best known in the art. Stoichiometrically stated, this method uses 1 equivalent of 3-chloropropylalkoxysilane and 2 equivalents of ethylene diamine for synthesizing 1 equivalent of 3-[N-(2-aminoethyl)]aminopropylalkoxysilanes, with ethylene diamine hydrochloride being formed at the same time, as shown by the following reaction scheme. ##STR1## In the formulae, each of R.sup.1 and R.sup.2 is an alkyl radical having 1 to 6 carbon atoms and n is equal to 1, 2 or 3.
In actual reaction, however, the end product 3-[N-(2-aminoethyl)]aminopropylalkoxysilanes further reacts with the starting reactants 3-chloropropylalkoxysilane and ethylene diamine to form bis-silyl products as shown below. ##STR2##
Various attempts were made to suppress side reactions since formation of these bis-silyl products remarkably lowers the yield of the end product 3-[N-(2-aminoethyl)]aminopropylalkoxysilane. For example, Japanese Patent Publication (JP-B) No. 1185/1965 discloses to react 4 to 6 equivalents of ethylene diamine with 1 equivalent of 3-chloropropylalkoxysilane. This method, however, is still insufficient in suppressing side reactions and low in the yield of the end product.
In JP-B 104891/1981, 7 to 10 equivalents of ethylene diamine is reacted with 1 equivalent of 3-chloropropylalkoxysilane. This method is effective for reducing formation of bis-silyl products and increasing the yield of the end product, but is a complex process since the excess ethylene diamine must be distilled out of the reaction system at the end of reaction. In addition, this method is low in production efficiency per batch since ethylene diamine is used in a large excess relative to 3-chloropropylalkoxysilane.
Also Japanese Patent Application Kokai (JP-A) Nos. 64031/1973 and 300192/1990 disclose a method for preparing 3-[N-(2aminoethyl)]aminopropylalkoxysilane by reacting hydroalkoxysilanes and N-allylethylene diamine in the presence of a platinum catalyst. This method, however, has the problem that the end product is of low purity because not only the end product 3-[N-(2-aminoethyl)]aminopropylalkoxysilane in gamma form is produced, but also beta form isomer, 2-[N-(2-aminoethyl)]amino-1-methylethylalkoxysilane is produced in large quantities. These isomers having approximate boiling points are difficult to separate.
Disclosed in JP-B 30313/1988 is a further method for preparing 3-[N-(2-aminoethyl)]aminopropylalkoxysilanes by reacting 2-cyanoethylalkoxysilanes with ethylene diamine and hydrogen gas in the presence of a heterogeneous catalyst of a metal selected from rhodium, platinum, and palladium. This method, however, requires to maintain high temperature and high pressure for a long period of time and is low in production efficiency per batch.